Astronaut wee could show us how the plumes on Enceladus work

It’s just a wee moon, but Saturn’s icy satellite Enceladus is one of the most promising places in the solar system in the hunt for alien life. Examining how spaceships vent urine could help us understand the small moon’s jets of water, which may spew out signs of life along with liquid.

At Enceladus’s south pole, plumes of liquid water and tiny ice shards spurt up from an ocean hidden under a thick sheath of ice. Despite the pictures we have of this region from NASA’s Cassini spacecraft, we don’t know much about the inner workings of the plumes because the probe could only detect one size of ice grain at a time, leaving scientists to guess at the overall distribution.

But Ralph Lorenz at Johns Hopkins University in Maryland says that we could use other jets of water in space – the ones formed as spacecraft release astronaut pee and waste water from fuel cells – as an analogue to better understand that distribution. He presented this work at the American Astronomical Society’s meeting of the Division of Planetary Sciences on 17 October.

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Whizzing water

When water whizzes out into the cold vacuum of space, some of it freezes instantaneously. In 1989, researchers at a telescope in Hawaii observed this process as the Discovery space shuttle dumped water from its fuel cells.

“There was a population of ice grains that were basically the size of the vent, but there’s a second population of much smaller grains that were interpreted as basically recondensing from the vapour,” says Lorenz. “That is probably the type of distribution that we’ll see on Enceladus.”

The plumes on Enceladus are far bigger and likely less uniform on the inside than a simple metal tube spraying out water, though. On the space shuttle, water being dumped formed long icicles on the outside of the nozzle in some cases, so the same may happen at Enceladus and change the structure of the vents over time, Lorenz says.

Urine vented from the space shuttle left a residue when tiny particles of wee ice hit the craft’s panels, so he suggests that future missions to Enceladus could have detectors that look for signatures of life in the miniscule dents left by ice grains there.

A bit of a stretch

“It seems like a stretch to me,” says Hunter Waite at the Southwest Research Institute in Texas. “The temperature of the water reservoir and how the liquid interacts with the ice walls that are several kilometres thick are important factors, and they don’t seem to have an analogue in this system.”

Lorenz says that even though the spacecraft water-dumping process is much simpler than Enceladus’s vents, it could still help us validate our models of the moon’s jets.

“These observations don’t tell us directly what’s happening on Enceladus, but they provide a sort of anchor for our interpretations of what we’re seeing on Enceladus and our designs for a new mission to go there,” says Lorenz.